1. Field of the Invention
This invention relates to a semiconductor laser array device. More particularly, it relates to a semiconductor laser array device which attains an optical intensity distribution with a minimized ripple of its far-field pattern and which produces high optical output power.
2. Description of the Prior Art
Semiconductor laser devices which are useful as light sources for optical discs, laser printers, optical measuring systems, etc., must produce high output power. However, conventional semiconductor laser devices having a single waveguide structure can only produce low output power, 60-70 mW at their best. In order to osillate laser lights in a array mode (i.e., a 0.degree. phase-shift mode, resulting in a single narrow beam with higher output power), semiconductor laser array devices, in which a plurality of waveguides are disposed in a parallel manner to achieve an optical phase-coupling between the adjacent waveguides, have been studied, for example, by D. R. Scifres, et al., Electronics Letters, Vol. 19, 169-171, 1983. However, their study of semiconductor laser array devices is focussed on the achievement of a single peak of the far-field pattern and/or the achievement of a single peak of the far-field pattern which approaches the diffraction limit, but it is not focussed on the achievement of the uniformity of the optical intensity distribution of the near-field pattern.
FIG. 4(a) shows the optical intensity distribution attained by a conventional semiconductor laser array device having a symmetrically branching waveguide structure. (Using this laser array device, single 0.degree. phase-shift mode oscillation was first observed by the inventors of this invention.) As seen from FIG. 4(a), the ripple index of the optical intensity distribution of the near-field pattern is around 90%, which has been reported by M. Taneya, et al., Applied Physics Letters, Vol. 47(4), 341-343, 1985.
FIG. 4(b) shows the optical intensity distribution of the near-field pattern in 180.degree. phaseshift mode oscillation attained by a conventional semiconductor laser array device. The ripple index thereof is 100%, which has been reported by M. Matsumoto, et al., Journal of Applied Physics, Vol. 58(7), 2783-2785, 1985.
Semiconductor laser array devices which are used for optical communication systems utilizing the image formation of the near-field pattern are required to achieve the uniformity of the optical intensity distribution of the near-field pattern.